Novel tertiary structures and stereospecificities of periplasmic binding proteins involved in active transport and chemotaxis.

Binding proteins, which are located in the periplasmic space of Gram-negative bacteria, are essential components of osmotic shock-sensitive active transport systems and Chemotaxis. Described briefly herein are the high resolution molecular structures of four binding proteins specific for (i) L-arabinose, (ii) sulphate, (iii) D-galactose, and (iv) leucine, isoleucine or valine which we have recently determined. The first three proteins contained bound substrates. Several novel substrate binding properties of the arabinose- and sulphatebinding proteins as revealed by structure refinement at 1·7 Å resolution are also presented. These results have profound significance in understanding both protein structures and substrate-protein interactions.